Single wafer type substrate cleaning method and apparatus

ABSTRACT

In the drying step of the single wafer type substrate cleaning system for cleaning wafers not stored in a cassette, in a sealed cleaning housing, a spin drying treatment is applied to the wafer when the wafer is supported and rotated at high speed while an inert gas for preventing oxidation is supplied to the face of the wafer, and the amount of the inert gas to be supplied to the face of the wafer is larger at the outer peripheral portion of the wafer than that supplied at the center thereof, thereby preventing oxidation on the face of the wafer effectively while optimizing the benefits of the single wafer type cleaning system.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The invention relates to a single wafer type substrate cleaningmethod and a single wafer type substrate cleaning apparatus, moreparticularly to a single wafer type wet cleaning technique or system forapplying a cleaning treatment to substrates such as semiconductor wafersone by one during the fabrication process as well as certain devicessuch as electronic parts and the like.

[0003] 2. Prior Art

[0004] A so-called batch type wet cleaning system has been the principalmethod of cleaning substrates such as semiconductor wafers (hereinafterreferred to simply as “Wafers”), whereby wafers stored in a carriercassette are immersed in sequence in wet bench type cleaning bathsarranged in series, or wafers are directly immersed in the cleaningbaths through a transfer unit without being stored in a carriercassette. However, semiconductor devices have reached the sub micronage, in that they are now micro-fabricated and highly integrated, suchthat the face of wafers has recently required a very high degree ofcleaning density, and wafers which are not stored in a cassette have tobe wet-cleaned individually in a sealed cleaning housing. To this end, aso-called single wafer type wet cleaning system intended to meet therequirement of a higher cleaning density has been developed.

[0005] Under the single wafer type wet cleaning system, wafers can becleaned with the use of a simple and compact cleaning system in arelatively clean atmosphere where particles and the like do not settleor remain on the face of the wafer. This system is therefore practicalto use for small scale production.

[0006] Under the single wafer type cleaning system, wafers can becleaned by the application of various chemical fluids on the face ofwafers in a predetermined order, and finally dried by a spin dryingtreatment whereby the wafers are rotated at high speed. However, thereare cases where oxygen remains in the sealed cleaning housing during thedrying treatment phase depending on the kind of chemical fluid used,such that the face of a wafer is prone to oxidization. Accordingly,improvement of the system is desirable.

SUMMARY OF THE INVENTION

[0007] The present invention has been made in view of the aforementionedconventional problems, and it is the object of the invention to providea single wafer type cleaning method capable of effectively preventingthe face of the wafer from becoming oxidized while optimizing thebenefits of the single wafer type wet cleaning system for individuallycleaning wafers which are not stored in a cassette in a sealed cleaninghousing.

[0008] Another object of the invention is to provide a single wafer typecleaning apparatus having the means of carrying out the single wafertype cleaning method set forth above as the first object of theinvention.

[0009] To achieve these objectives, the proposed method comprises theapplication of a spin drying treatment to the wafer when the wafer issupported and rotated at high speed while an inert gas for preventingoxidation is supplied to the face of the wafer during the dryingprocess, and the inert gas supplied to the face of the wafer is suchthat the amount supplied at the outer region of the wafer is larger thanthat supplied at the center thereof.

[0010] In the preferred embodiment, a sealed drying space is intended tobe formed at the outer region of the face of the wafer and inert gas issupplied to the inside of the sealed drying space, wherein the inert gasis a nitrogen gas (hereinafter referred to as “N₂ gas”).

[0011] Further, the single wafer type cleaning apparatus of theinvention which is deemed suitable for carrying out the foregoingcleaning method comprises (1) a wafer rotary means for supporting androtating a single wafer in a horizontal position in the cleaninghousing; (2) a cleaning chamber provided at the outer region of thewafer rotary means for the purpose of forming a cleaning treatment spacefor the wafer which is rotatably supported by the wafer rotary means;(3) a chemical fluid supply means for supplying cleaning fluid to theface of the wafer which is rotatably supported by the wafer rotarymeans; (4) and an inert gas supply means for supplying N₂ gas intendedto prevent oxidation on the face of the wafer which is rotatablysupported by the wafer rotary means, wherein the supply port of theinert gas supply means is designed in such a manner that the amount ofN₂ gas supplied to the outer region of the face of the wafer is largerthan that at the center thereof.

[0012] In the preferred embodiment, the inert gas supply means has a gasinjection section consisting of a circular cover body intended to form asealed drying space at the outer region of the face of the wafer whichis rotatably supported by the wafer rotary means while cooperating withthe cleaning chamber, wherein the gas injection section comprises a flathollow body which communicates with an inert gas supply source at theinside thereof and the supply port at the plane bottom portion.

[0013] The supply port of the gas injection section comprises aplurality of injection openings which are disposed radially and arrangedconcentrically with the face of the wafer, which is rotatably supportedby the wafer rotary means, and these injection openings are designed insuch a manner that the sum of the areas of the injection openings at theouter region of the face of the wafer is larger than that at the centerthereof as the injection openings direct toward the outer region of thewafer.

[0014] Further, a baffle plate is interposed in the hollow section ofthe gas injection section to prevent the inert gas from directly flowingto the center of the supply port of the inert gas.

[0015] Under the single wafer type cleaning system of the invention, theface of the wafer is cleaned by employing various chemical fluids in thesealed cleaning housing in a predetermined order, and finally the waferis dried through a spin drying treatment while the wafer is rotated athigh speed, in which case, oxygen will likely remain in the sealedcleaning chamber during the drying process depending on the kind ofchemical fluid(s) used, resulting in oxidation on the face of the wafer.

[0016] To address the foregoing problem, the invention proposes toprovide a spin drying treatment to the wafer which is supported androtated by the wafer rotary means at high speed while being suppliedwith N₂ gas for preventing oxidation on the face of the wafer.

[0017] The degree of oxidation on the wafer depends on the concentrationof oxygen in the circum-ambient atmosphere on the face of the wafer, andit has been found, as a result of research and tests conducted by theinventors, that concentration of oxygen in the circum-ambient atmosphereon the face of the wafer is higher at the outer peripheral portion ofthe face of the wafer than that at the center thereof in an ordinarystate.

[0018] It is thus necessary to make the concentration of oxygen at theouter peripheral portion of the face of the wafer to become zero (0) orclose to zero (0) so as to prevent oxidation on the wafer, and toachieve this, the cleaning housing should be purged by supplying N₂ gasto the inside thereof. This however requires a considerable volume of N₂gas which would increase running costs and is therefore uneconomical.

[0019] According to the invention, the amount of N₂ gas to be suppliedto the face of the wafer must be such that the amount supplied to theouter peripheral portion of the wafer is larger than that at the centerthereof so that concentration of oxygen is allowed to become zero (0) orclose to zero (0) while reducing the usage of N₂ gas as much as possiblein order to prevent oxidation on the face of the wafer.

[0020] Described more in detail, the drying process of the single wafertype cleaning system for individually cleaning wafers which are notstored in a cassette in the sealed cleaning housing, entails the supportand rotation of the wafer at high speed by the wafer rotary means,thereby applying a spin drying treatment to the wafer while N₂ gas forpreventing oxidation is supplied to the face of the wafer, and theamount of inert gas supplied to the face of the wafer is such that theamount of inert gas supplied to the outer peripheral portion of thewafer is larger than that at the center thereof. Accordingly, it ispossible to improve and enhance the usefulness of the single wafer typecleaning system by providing a method of effectively preventingoxidation on the face of the wafer.

[0021] That is, under the single wafer type cleaning system, the waferis cleaned by the introduction of various chemical fluids in the sealedcleaning housing in a predetermined order, and finally dried through aspin drying treatment while the wafer is rotated at high speed, andsimultaneously supplying an N₂ gas for preventing oxidation on thewafer. The degree of oxidation that develops on the wafer depends on theconcentration of oxygen in the circum-ambient atmosphere on the face ofthe wafer.

[0022] According to the invention therefore, if the amount of N₂ gassupplied to the face of the wafer is such that the amount of N₂ gassupplied to the outer peripheral portion of the wafer is larger thanthat at the center thereof, the concentration of oxygen is substantiallyreduced to zero (0) or close to zero (0) while the usage of N₂ gas isdecreased as much as possible, thereby preventing oxidation on the faceof the wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 is a front sectional view showing the internal constructionof a single wafer type cleaning apparatus according to the preferredembodiment of the invention;

[0024]FIG. 2 is an enlarged sectional front view showing the locationalrelationship between the wafer rotary section and the inert gas supplysection of the single wafer type cleaning apparatus;

[0025]FIG. 3 is an enlarged sectional front view showing the locationalrelationship between the wafer rotary section and the inert gas supplysection in the drying step;

[0026] FIGS. 4(A) to (C) are bottom views respectively showing concreteconstructions of the injection openings of the gas injection section inthe inert gas supply section; and

[0027]FIG. 5 is a view showing the distribution of the concentration ofoxygen in the circum-ambient atmosphere on the face of a wafer which issupported by a wafer supporting section of the wafer rotary section inan ordinary state.

PREFERRED EMBODIMENT OF THE INVENTION

[0028] The preferred embodiment of the invention is described withreference to the attached drawings.

[0029] A single wafer type cleaning apparatus is illustrated in FIG. 1,wherein each wafer W, which is not stored in a cassette, is wet-cleanedindividually in a sealed cleaning housing 1, and the sealable cleaninghousing 1 comprises a wafer rotary section (wafer rotary means) 2 forrotatably supporting one wafer W in the horizontal position, a cleaningchamber 3 which is relatively vertically movable, a chemical fluidsupply section (chemical fluid supply means) 4 for supplying thecleaning fluid, an inert gas supply section (inert gas supply means) 5for supplying the N₂ gas for oxidation prevention, and a controller 6for controlling these driving sections while interlocking mutuallytherewith as major components.

[0030] The cleaning housing 1 is sealable at the upper portion for thecleaning treatment and serves as a location for installing various unitdriving sections at the lower portion disposed in the upper space. Aclosable wafer taking in-out port, not shown in detail, through whichthe wafer W is taken in or taken out in the upper space of the cleaninghousing 1, is structured in such a way to secure airtightness andwatertightness when it is closed.

[0031] The wafer rotary section 2 horizontally rotates a single wafer Wwhile it supports the single wafer W in the horizontal position when thespin cleaning and spin drying treatments are applied thereto, and itcomprises a rotary shaft 10, a wafer supporting section 11 which isattached to and supported by the upper end portion of the rotary shaft10 in the horizontal position, and a driving motor 12 for rotatablydriving the rotary shaft 10.

[0032] The wafer supporting section 11 and the rotary shaft 10 arerotatably disposed at the center of the cleaning housing 1 via a bearingsupporting cylinder 13 in a perpendicular position, and a single wafer Wcan be supported by the wafer supporting section 11 in the horizontalstate.

[0033] In particular, the wafer supporting section 11 is provided with awafer mounting section 14 for mounting and supporting the peripheraledge of the wafer W as shown in FIGS. 2 and 3.

[0034] The wafer mounting section 14 is supported horizontally by thewafer supporting section 11 and is composed of a cup body which isinclined at the peripheral edge thereof and rises towards the outerregion. The wafer mounting section 14 has a plurality of claws 14 a, 14a, etc. for supporting the outer edge of the wafer W. The claws 14 a, 14a, etc. of the wafer mounting section 14 are designed to have the sameheight, in order that the peripheral edge of the wafer W can besupported in the horizontal position. The supporting face of each claw14 a has a configuration corresponding to the contour of the peripheraledge of the wafer W in cross section, and the peripheral edge cornersection of each claw 14 a can contact and support the square peripheraledge of the wafer W in cross section in a point contact state or linecontact state.

[0035] The rotary shaft 10 is rotatably supported by the bearingsupporting cylinder 13 in the standing position, and the lower endportion of the rotary shaft 10 is connected to the driving motor 12 soas to be rotatably driven by the driving motor 12 via a belt entrainedtherebetween so that the wafer supporting section 11 is rotated at agiven speed of rotation. The speed of rotation of the rotary shaft 10 isset at low speed, e.g., 40-50 r.p.m. when the spin cleaning treatment iseffected while it is set at high speed of 3000 r.p.m. when the spindrying treatment is effected.

[0036] The cleaning chamber 3 is the section where the cleaningtreatment is applied to the wafer W, and the inner diameter dimensionsthereof are determined in connection with the wafer supporting section11 of the wafer rotary section 2, described hereinbelow, and has acleaning treatment space for the wafer W, which is rotatably supportedby the wafer rotary section 2, at the outer region of the wafer rotarysection 2.

[0037] In detail, the cleaning chamber 3 has plural stages of annulartreatment baths 15 to 18 which are arranged vertically at the innerperiphery thereof as shown in FIGS. 1 and 2, and is constructed to moveup and down vertically relative to the wafer rotary section 2.

[0038] In the illustrated preferred embodiment, the four stages ofannular treatment baths 15 to 18 are arranged vertically andconcentrically with the wafer W so as to surround the wafer W which issupported by the wafer supporting section 11 of the wafer rotary section2.

[0039] The peripheral inner edges of the annular treatment baths 15 to18 are arranged in the manner that annular gaps defined between theseedges are set to have small intervals to such extent for preventing thechemical fluid(s) and the like from being leaked downward and at thesame time do not contact the outer diameter edge of the wafer supportingsection 11 of the wafer rotary section 2.

[0040] The cleaning chamber 3 is constructed to be movable up and down,i.e., vertically via an elevating guide (not shown), and has anelevating mechanism 20 capable of elevating relative to the wafersupporting section 11 of the wafer rotary section 2 by a given stroke.

[0041] The elevating mechanism 20 comprises a feed screw mechanism (notshown), which moves a supporting frame 21 for supporting the cleaningchamber 3 up and down, and a driving motor 22 for rotatably driving thefeed screw mechanism.

[0042] Depending on the cleaning treatment step, the cleaning chamber 3is moved up and down vertically by a given stroke via the feed screwmechanism when the driving motor 22 is driven while interlocking withthe operation of the wafer rotary section 2, described hereinbelow, sothat any one of the annular treatment baths 15 to 18 for effecting thecleaning treatment step may be selected from a position of heightrelative to the wafer W which is supported by the wafer supportingsection 11 of the wafer rotary section 2.

[0043] Drain sections, which communicate with the outside of theapparatus, are respectively provided in the four annular treatment baths15 to 18 (not illustrated in detail). These drain sections discharge thechemical fluid(s) or the inert gas inside the annular treatment baths 15to 18, in which they are structured to be opened only when the cleaningtreatment is effected and to be closed when the cleaning treatment iseffected in the other treatment baths.

[0044] The chemical fluid supply section 4 supplies the chemicalfluid(s) to the face of the wafer W which is rotatably supported by thewafer rotary section 2, and it is provided on the upper portion of thecleaning housing 1 and can communicate with the chemical fluid supplysource 25 provided outside the cleaning housing 1.

[0045] The chemical fluid supply section 4 is composed of injectionnozzles for injecting and supplying cleaning fluid(s) to the face of thewafer W from above, which wafer W is rotatably supported by the wafersupporting section 11 of the wafer rotary section 2. The chemical fluidsupply section 4 is structured so that it may be turned horizontally ina downward direction over the cleaning housing 1, and it is directlyconnected to a driving motor capable of being swung (not shown).

[0046] The chemical fluid supply section 4 is constructed to inject andsupply the cleaning fluid to the face of the wafer W which is rotatablysupported by the wafer supporting section 11 of the wafer rotary section2 in the horizontal position while the face of the wafer is turnedhorizontally from its outer peripheral portion toward the centerthereof.

[0047] In the illustrated preferred embodiment shown in FIGS. 1 to 5,the chemical fluid supply section 4 has nozzle ports each of which isidentified by a number corresponding to the kind of cleaning fluid(s) tobe supplied. In particular, three nozzle ports are provided (not shown)intended to serve as supply ports for an APM fluid, purified water and aDHF fluid Injection nozzles 26 are opened at the upper end portion ofthe rotary shaft 10 corresponding to the chemical fluid supply section4, have the same number of nozzle ports as those of the chemical fluidsupply section 4, i.e., three nozzle ports, and are constructed in sucha way as to inject and supply cleaning fluid to the back face of thewafer W from the lower side. The injection nozzles 26 can communicatewith the fluid supply source 25 via an internal pipe of the rotary shaft10, and serve as supply ports for an APM fluid, purified water and a DHFfluid.

[0048] As a result, the wafer W can be cleaned at the front and backfaces thereof at the same time or selectively.

[0049] The inert gas supply section 5 supplies the inert gas forpreventing oxidation on the face of each wafer W which is rotatablysupported by the wafer rotary section 2 and can communicate with aninert gas supply source 27 provided on the upper portion of the cleaninghousing 1. In the illustrated preferred embodiment, a N₂ gas is used asthe inert gas.

[0050] The inert gas supply section 5, as shown in FIG. 3 in detail, isprovided with a gas injection section 30 composed of a circular coverbody forming the drying sealed space A at the outer region of the faceof the wafer W which is rotatably supported by the wafer rotary section2 while cooperating with the cleaning chamber 3.

[0051] The outer periphery of the gas injection section 30, as shown inFIG. 3, is designed to engage with the inner peripheral portion of thecleaning chamber 3, namely, the outer periphery of the uppermost stagetreatment bath 18, whereby the sealed drying space A of necessaryirreducible minimum volume is formed at the outer peripheral portion ofthe face of the wafer W which is rotatably supported by the wafer rotarysection 2.

[0052] The gas injection section 30 comprises a flat hollow bodycommunicating with the inert gas supply source 27 via a communicationpipe 33 at the inside thereof, and has a supply port 32 at its bottomportion as viewed from the above, namely, from the bottom plate 31consisting of a flat plate.

[0053] The supply port 32 comprises a plurality of injection openings 32a, 32 a, etc. which are radially disposed and concentrically arrangedwith the face of the wafer W which is rotatably supported by the waferrotary section 2 (see FIG. 4), and structured in such a manner that theamount of N₂ gas supplied to the face of the wafer W at the outerperipheral portion of the wafer W is larger than that at the centerthereof. The rationale for the construction of the supply port 32 isstated hereinbelow.

[0054] That is, the degree of oxidation on the wafer W depends on theconcentration of oxygen in the circum-ambient atmosphere on the face ofthe wafer W, and it has been found, as a result of research and testsconducted by the inventors, that concentration of oxygen on the face ofthe wafer W in the circum-ambient atmosphere thereof is higher at theouter peripheral portion of the face of the wafer W than that at thecenter thereof in an ordinary state as it directs toward the outerregion of the wafer W, as shown in FIG. 5.

[0055] It is therefore necessary to make the concentration of oxygen atthe outer peripheral portion of the face of the wafer to become zero (0)or close to zero (0) in order to prevent oxidation on the wafer W, andto attain this objective, the cleaning housing must be entirely purgedby supplying inert gas to the inside of the cleaning housing 1 which, aspreviously stated, requires a considerable volume of inert gas whichwould increase running costs and is therefore uneconomical.

[0056] Likewise, as already stated hereinabove, the amount of inert gassupplied to the face of the wafer must be such that the amount suppliedto the outer peripheral portion of the wafer is larger than that at thecenter thereof so that concentration of oxygen is substantially reducedto zero (0) or close to zero (0) while decreasing the usage of the inertgas as much as possible, thereby realizing the objective of preventingoxidation on the face of the wafer.

[0057] In order to concretely determine the amount of inert gas to besupplied to the face of the wafer W, it has been proposed that the sumof the areas of these injection openings 32 a, 32 a, etc. at the outerperipheral portion of the wafer W is larger than that at the centerthereof and examples are shown in FIGS. 4(A), (B), (C) as the injectionopenings direct toward the outer peripheral portion of the wafer W.

[0058] That is, the injection openings 32 a, 32 a, etc. shown in FIG.4(A) are composed of arc slits, and the length and width dimensions ofsuch arc slits are determined to be larger at the outer peripheralportion of the face of the wafer W than those at the center thereof asthe injection openings direct toward the outer peripheral portion of thewafer W.

[0059] Further, the injection openings 32 a, 32 a, etc. shown in FIG. 4(B) are composed of radially extended slits, and the width dimensions ofsuch slits at the outer peripheral portion of the face of the wafer Ware determined to be larger than those at the center thereof as theinjection openings direct toward the outer peripheral portion of thewafer W.

[0060] Further, the injection openings 32 a, 32 a, etc. shown in FIG. 4(C) consist of circular openings which are arranged circumferentiallyand radially at prescribed intervals, and the diameter dimensionsthereof are determined to be larger at the outer peripheral portion ofthe face of the wafer W than those at the center thereof as theinjection openings direct toward the outer peripheral portion of thewafer W.

[0061] Alternatively, although not shown, the number of disposition ofthe injection openings 32 a, 32 a, etc. is determined to be larger atthe outer peripheral portion of the face of the wafer W than that at thecenter thereof, or, the number of disposition of the injection openings32 a, 32 a, etc. may be combined with the construction of the areas ofopenings shown in FIGS. 4(A) to (C).

[0062] Although the amount of inert gas to be supplied can be controlledeven by merely setting the number of disposition or areas of openings ofthe injection openings 32 a, 32 a, etc. according to the invention, abaffle plate 35 is interposed in the hollow section of the gas injectionsection 30 in addition to the construction set forth above.

[0063] The baffle plate 35 prevents the N₂ gas from directly flowing tothe center of the supply port 32, and it consists of a discoid platehaving a diameter smaller than the bottom plate 31 of the gas injectionsection 30.

[0064] The N₂ gas supplied to the inside of the gas injection section 30via the communication pipe 33 flows to an outer peripheral edge alongthe upper face of the baffle plate 35 and turns around the outerperipheral edge, then reaches the supply port 32 of the bottom plate 31so that a considerable volume of N₂ gas can be supplied to the outerregion of the supply port 32.

[0065] Accordingly, the number of disposition and the areas of openingsof the injection openings 32 a, 32 a, etc. constituting the supply port32 have been designed considering the operation of the baffle plate 35,thereby prescribing a flow rate model of the N₂ gas to achieve a zero(0) concentration of oxygen in the circum-ambient atmosphere on the faceof the wafer W (see arrows in FIG. 2) while reducing the usage of N₂ gasas much as possible.

[0066] Further, the gas injection section 30 is movable up and downbetween a use position, where it cooperates with the cleaning chamber 3,i.e., the height position shown in FIG. 3, and a use standby position,where the gas injection section 30 does not interfere with the chemicalfluid supply section 4, i.e., the height position shown in FIG. 1, anddrivably connected to an elevating means, not shown.

[0067] The fluid supply source 25 is intended to supply a chemical fluidfor cleaning to the chemical fluid supply section 4, i.e., injectionnozzles 4 and 26, and has two chemical fluid systems, in the illustratedembodiment, by which the wafer W is to be cleaned with APM fluid(NH₄OH+H₂O₂+H₂O) or with DHF fluid (HF+H₂O). Annular treatment baths 15to 18 in the cleaning chamber 3 correspond to these two chemical fluidsystems, namely, the lowermost stage treatment bath 15 is used for thecleaning step by APM fluid, the third upper stage treatment bath 16 isused for the cleaning step by DHF fluid, the second upper stagetreatment bath 17 is used for the rinsing step by purified water, andthe uppermost stage treatment bath 18 is used for the spin drying step.

[0068] Under the single wafer type cleaning apparatus having theaforedescribed construction, when the cleaning chamber 3 is moved up anddown, either the wafer W supported by the wafer supporting section 11 ofthe wafer rotary section 2 or the circular treatment baths 15 to 18 ofthe cleaning chamber 3 are selectively positioned, and the wafer Wsupported by the wafer supporting section 11 is horizontally rotatableby the wafer rotary section 2 at a prescribed speed of rotation.

[0069] The chemical fluid supply source 27 is constructed to selectivelyeffect cleaning steps of i) APM+DHF+(O₃+DIW)+DRY, ii) APM+DHF+DRY, iii)APM+DRY, DHF+DRY or the like, with the cooperation of the inert gassupply source 37, described hereinbelow, by appropriately selectivelysetting a recipe for cleaning steps.

[0070] The controller 6 controls the movement of these components of thesingle wafer type cleaning apparatus while interlocking with thesecomponents, so that the following series of wet treatment steps areautomatically effected:

[0071] (1) The wafer W, before the cleaning treatment is appliedthereto, is placed in the wafer supporting section 11 inside thecleaning chamber 3 via the wafer taking in/out port of the cleaninghousing 1, (not shown), and when the cleaning chamber 3 is sealed, thewafer W is positioned at the wafer cleaning treatment position insidethe cleaning chamber 3 when the cleaning chamber 3 is moved up and down,and then various cleaning treatments are effected in a predeterminedprocedure.

[0072] (2) For example, if the cleaning treatment is in the foregoingii) cleaning treatment step (APM+DHF+DRY), the wafer W on the wafersupporting section 11 is positioned and disposed in the lowermost stagetreatment bath 15 when the cleansing chamber 3 is moved up and down insuch a way that the APM fluid is supplied from the injection nozzle 4,and a spin cleaning treatment is applied to the wafer W when the waferrotary section 2 is rotated at low speed.

[0073] (3) Subsequently, the wafer W is positioned and disposed in thesecond upper stage treatment bath 17, and purified water is suppliedfrom the injection nozzle 4 and a rinsing treatment is applied to thewafer W when the wafer rotary section 2 is rotated at low speed.

[0074] (4) Further, the wafer W is positioned and disposed in the thirdupper stage treatment bath 16, and the DHF fluid is supplied from theinjection nozzle 4 and a spin cleaning treatment is applied to the waferW when the wafer rotary section 2 is rotated at low speed.

[0075] (5) Further, the wafer W is positioned and disposed in the secondupper stage treatment bath 17, and purified water is supplied from theinjection nozzle 4, and a rinsing treatment is applied to the wafer Wwhen the wafer rotary section 2 is rotated at low speed.

[0076] (6) Finally, the wafer W is positioned and disposed in theuppermost stage treatment bath 18, and a spin drying treatment isapplied to the wafer W when the wafer rotary section 2 is rotated athigh speed.

[0077] In the drying step, the gas injection section 30 of the inert gassupply section 5 is lowered to a position shown in FIG. 3 to cooperatewith the cleaning chamber 3 so as to form the sealed drying space A andthen the N₂ gas is supplied to the sealed drying space A. The amount ofN₂ gas supplied to the face of the wafer W is such that the amount of N₂gas supplied to the outer peripheral portion of the face of the wafer Wis larger than that at the center thereof.

[0078] Accordingly, when the inside of the sealed drying space A iscleaned by the N₂ gas, or when occasion demands, air current is producedin the passageway extending from the inert gas supply section 5 to thedrain section inside the sealed drying space A owing to the forcefuldischarge of the N₂ from the drain section of the uppermost stagetreatment bath 18, concentration of oxygen at the entire outer region ofthe face of the wafer W is reduced to zero (0) or close to zero (0),when the spin drying treatment is applied to the wafer W.

[0079] (7) The wafer W is again taken out via the wafer taking in/outport of the cleaning housing 1 upon completion of a series of cleaningtreatments in the wafer cleaning apparatus.

[0080] Under the single wafer type cleaning apparatus constructed in theaforedescribed manner, the cleaning steps by the utilization of variouskinds of chemical fluids are effected relative to the face of the waferW in the sealed cleaning housing 1 in a predetermined order. Thereafter,the drying step proceeds through the spin drying treatment by which thewafer W is rotated at high speed by the wafer rotary section while an N₂gas is supplied to the face of the wafer W the wafer W, therebypreventing oxidation on the wafer W.

[0081] In this case, the N₂ gas supplied to the face of the wafer W issuch that the amount of N₂ gas supplied to the outer peripheral portionof the face of the wafer W is larger than that at the center thereofthereby reducing the usage of the N₂ gas as much as possible to allowthe concentration of oxygen to become zero (0) or close to zero (0),thereby preventing oxidation on the face of the wafer W.

[0082] Although the foregoing embodiment is the preferred embodiment ofthe invention, the invention is not limited thereto but can be designedand modified in various ways within the scope of the invention.

[0083] For example, the wafer cleaning apparatus can be used as a singleapparatus, or as a basic construction element of a wafer cleaning systemprovided with a loading section, an unloading section or other types ofequipment such as placing and mounting robots and the like. Further, thechemical fluids employed by the preferred embodiment are merely samples,and hence other chemical fluids such as HPM (HCL+H₂O₂+H₂O), SPM(H₂SO₄+H₂O₂+H₂O) and the like can be used depending on the objectthereof.

What is claimed is:
 1. A single wafer type substrate cleaning method ofwet-cleaning wafers which are not stored in a cassette, individually, ina sealed cleaning housing, said method consisting of the application ofa spin drying treatment to the face of each wafer by supporting androtating each wafer at high speed in the sealed cleaning housing whilean inert gas for preventing oxidation is supplied to the face of thewafer in a drying step, where the amount of inert gas to be supplied tothe face of each wafer is such that the amount of inert gas supplied atthe outer peripheral portion is larger than that at the center thereof.2. The single wafer type substrate cleaning method according to claim 1,wherein a sealed drying space is formed at the outer peripheral portionof the face of the wafer and the inert gas is supplied to the inside ofthe sealed drying space so that the space is filled with inert gas. 3.The single wafer type substrate cleaning method according to claim 1,wherein the inert gas employed is a nitrogen gas.
 4. A single wafer typesubstrate cleaning apparatus for cleaning wafers, which are not storedin a cassette, one by one in a sealed cleaning housing, said apparatuscomprising of: a wafer rotary means for supporting and rotating a singlewafer in the cleaning housing in the horizontal position; a cleaningchamber provided at the outer peripheral portion of the wafer rotarymeans for forming a cleaning treatment space for cleaning each waferwhich is rotatably supported by the wafer rotary means; a chemical fluidsupply means for supplying cleaning fluid(s) to the face of the waferwhich is rotatably supported by the wafer rotary means; and an inert gassupply means for supplying inert gas to prevent oxidation on the face ofthe wafer which is rotatably supported by the wafer rotary means;wherein the number of supply ports of the inert gas supply means is suchthat the number of supply ports at the outer peripheral portion of theface of the wafer is larger than that at the center thereof.
 5. Thesingle wafer type substrate cleaning apparatus according to claim 4,wherein the inert gas supply means has a gas injection sectionconsisting of a circular cover body for forming the sealed drying spaceat the outer peripheral portion of the face of the wafer which isrotatably supported by the wafer rotary means while cooperating with thecleaning chamber, wherein the gas injection section comprises a flathollow body which communicates with an inert gas supply source at theinside thereof and has the supply ports at the plane bottom portion. 6.The single wafer type substrate cleaning apparatus according to claim 5,whereby the supply ports of the gas injection section comprise aplurality of injection openings which are disposed radially and arrangedconcentrically with the face of the wafer, and the sum of the areas ofopenings of these injection openings is determined to be larger at theouter peripheral portion of the face of the wafer than that at thecenter thereof as the injection openings direct toward the outerperipheral portion of each wafer.
 7. The single wafer type substratecleaning apparatus according to claim 6, wherein the area of theinjection openings is determined to be larger at the outer region of theface of the wafer than at the center thereof as the injection openingsdirect toward the outer region of the wafer.
 8. The single wafer typesubstrate cleaning apparatus according to claim 6, wherein the number ofdisposition of the injection openings is determined to be larger at theouter region of the face of the wafer than at the center thereof as theinjection openings direct toward the outer peripheral portion of thewafer.
 9. The single wafer type substrate cleaning apparatus accordingto claim 6, further comprising a baffle plate which is interposed in thehollow section of the gas injection section for preventing the inert gasfrom directly flowing to the central portions of the supply ports of theinert gas.
 10. The single wafer type substrate cleaning apparatusaccording to any of claims 5 to 9, wherein the gas injection section ismovable between a use position where it cooperates with the cleaningchamber and a standby position where it does not interfere with thechemical fluid supply means.
 11. The single wafer type substratecleaning apparatus according to any of claims 4 to 10, wherein thecleaning chamber is movable up and down relative to the wafer rotarymeans, and the plural stages of the annular cleaning baths forming thecleaning treatment space are arranged vertically in and concentricallywith the inner peripheral portion of the cleaning chamber so as tosurround the wafer supported by the wafer rotary means, and wheredepending on the cleaning treatment step to be employed, one of thecircular treatment baths is accordingly moved to a positioncorresponding to the wafer supported by the wafer rotary means when thecleaning chamber is moved up and down.
 12. The single wafer typesubstrate cleaning apparatus according to any of claims 4 to 11, whereinthe cleaning chamber is designed in such a manner that the innerperipheral portion of each annular treatment bath does not contact theouter periphery of the wafer supporting section of the wafer rotarymeans, and the annular gap defined between these edges is at very smallintervals to prevent chemical fluids and purified water from beingleaked downward.
 13. The single wafer type substrate cleaning apparatusaccording to any of claims 4 to 12, wherein the chemical fluid supplysection consists of injection nozzles for injecting and supplyingcleaning fluid to the face of each wafer which is supported by the waferrotary means from above, and the injection nozzles are provided to behorizontally turnable while directed downward, and inject and supply thecleaning fluid to the face of each wafer which is rotatably supported bythe wafer rotary means while it is turned horizontally from the outerperipheral portion toward the center thereof or in standstill positionas it is horizontally turned.
 14. The single wafer type substratecleaning apparatus according to any of claims 4 to 13, wherein the inertgas is a nitrogen gas.